An elastic wave resonator has comb-shaped electrodes that have been formed from an aluminum alloy, a Cu alloy, or the like on a piezoelectric substrate, a piezoelectric thin film, or the like and that have a period corresponding to a predetermined frequency, and the elastic wave resonator makes use of elastic waves excited by the comb-shaped electrodes. The comb-shaped electrode is called IDT (Interdigital transducer). Examples of elastic waves excited by comb-shaped electrodes are surface acoustic waves and elastic boundary waves. For example, in the case of a 1 port resonator, a dual resonance characteristic of having a resonance frequency and an antiresonance frequency is exhibited. An example of a circuit employing this characteristic is a ladder filter in which 1 port resonators that have different comb-shaped electrode periods are disposed in series arms and parallel arms to form a ladder shape (e.g., see Patent Document 1). Other examples include a DMS (Double mode SAW (Surface Acoustic Wave)) filter in which a resonator is formed by a plurality of comb-shaped electrodes, and an IIDT (Interdigitated IDT) filter that has excitation comb-shaped electrodes and reception comb-shaped electrodes.
FIG. 15A is a circuit diagram illustrating a basic configuration of a ladder filter, and FIG. 15B is a top view of the ladder filter in FIG. 15A. In the ladder filter, series resonators 102, 103, and 104 connected in series arms and parallel resonators 105, 106, and 107 connected in parallel are formed between an input terminal 101 and an output terminal 108. The series resonator 102 and the parallel resonator 105, the series resonator 103 and the parallel resonator 106, and the series resonator 104 and the parallel resonator 107 respectively configure one-stage filters, and the one-stage filters are connected in multiple stages (three stages). The input terminal 101 and the output terminal 108 in FIG. 15A are configured by an input bump 112 and an output bump 113 in FIG. 15B, and the grounds in FIG. 15A are configured by ground bumps 114, 115, and 116 that are grounded in FIG. 15B.
A ladder filter is used in a duplexer connected to an antenna of a communication apparatus. Accordingly, particularly in the case of a transmission ladder filter, there is demand for power durability due to being directly subjected to the power transmitted to the antenna. In a ladder filter, a first method of raising the power durability by design involves suppressing the occurrence of migration by raising the ability of the device to exhaust heat and lowering the temperature of the device.
Heat is exhausted from the piezoelectric substrate by allowing the heat to escape to a connection substrate mainly via a package or the like. In a conventional configuration, as illustrated in the top view of FIG. 16A and the cross-sectional diagram of FIG. 16B, a piezoelectric substrate 121 configuring a filter is bonded to a package 123 via a die bonding material 122, and heat is exhausted from the entire back face of the piezoelectric substrate 121 to the package 123. Furthermore, heat is allowed to escape from the package 123 to the connection substrate (not illustrated). Electrodes on the piezoelectric substrate 121 are connected to electrodes 124 of the package 123 via wires 125.
Also, a reduced-size package has, as illustrated in the top view of FIG. 17A and the cross-sectional diagram of FIG. 17B, a flip chip bonding (FCB) configuration in which gold bumps 132 formed on a piezoelectric substrate 131 on which a filter is formed are connected to a package 133 using a face-down method in order to achieve a small size and low profile, and heat is exhausted to the package 133 via the gold bumps 132.
Also, a second method of improving the power durability involves increasing the number of pairs (number of comb-shaped electrodes) per resonator. FIG. 18 is a top view illustrating a structure of a 1 port resonator. The 1 port resonator has a piezoelectric substrate 141, a resonation unit 143, and reflectors 142. The resonation unit 143 has two opposing excitation electrodes 144 and 145. An electrostatic capacitance C0 of the resonator is determined according to the number of pairs in the excitation electrodes 144 and 145, and the impedance of the filter is determined according to the electrostatic capacitance. Raising the number of pairs more than necessary therefore changes the impedance of the filter. In view of this, as illustrated in the top view illustrated in FIG. 19, two resonators, each having a resonation unit 146 having excitation electrodes 147 and 148 having a doubled number of pairs, are connected in series, and therefore there is no change in the capacitance with respect to the two resonators, the number of pairs in each of the resonators is doubled, and the power durability is improved.    Patent document 1: Japanese Laid-open Patent Publication 7-122961
However, problems such as the following exist in the conventional filters described above. With the first method for raising the power durability, the heat conductivity per bump is good since gold is used, but the number of heat exhaust paths is reduced, and the temperature of the filter rises. For this reason, in order to efficiently exhaust heat, it is important to dispose the bumps beside the heat generating elements (comb-shaped electrodes). FIG. 20 is a top view of a 1 port resonator. Wiring (not illustrated) for supplying power to the electrodes is drawn around in regions 149 where a bump cannot be disposed. Regions 150 where a bump can be disposed are regions on sides of reflectors 142 that are outward with respect to a resonation unit 143, and since such regions are separated from the center (the circle in the figure) of the heat generating elements, it is difficult for heat to be exhausted efficiently.
Also, with the second method for raising the power durability, the size of the resonator itself increases, thus having the problem that the device size increases. Also, since the regions where a bump can be disposed are separated from the center of the heat generating elements, there are problems such as a weakening of the effect of exhausting heat via the bumps.